Clinical and necropsy findings are described in 40 patients who had aortic dissection with the entrance tear in the descending thoracic aorta. Their ages at death ranged from 39 to 91 years (mean 66); 24 (60%) were men and 16 (40%) were women. Systemic hypertension was present by history in 33 patients (83%) and the hearts were of increased weight in 78%. Of the 40 patients, 31 (78%) had no operative intervention, while 9 (22%) underwent operation for aortic dissection. Of the 31 patients without operative therapy, the diagnosis of aortic dissection was established in life in 9 (29%). The interval from aortic dissection to death was < 30 days in 13 patients (42%); rupture of the false channel was the cause of death in 9 (69%), renal failure in 2 (15%), and the cause was unclear in 2 (15%). The interval from aortic dissection to death was > 30 days in 18 (58%) of the 31 patients without operative therapy. The cause of death in these 18 patients was related to the dissection in 11 (61%) (rupture of the false channel in 5; renal failure from dissection in 3, and rupture of the false channel of a second acute dissection in 3); death in the other 7 patients (39%) was unrelated to the dissection but a non-fatal complication, namely stenosis of the true channel from compression by a thrombus-filled false channel, occurred in 4 of these 7 patients. Thus, only 3 (10%) of the 31 patients without operative therapy had no complications of aortic dissection. All 9 patients who underwent operation had an aortic dissection within 30 days, and the operation was performed because of a major complication of the dissection. Four patients survived 8 to 84 months after operation.